For effective washing of clothing products and the like, it is important to sufficiently detach dirt materials from the object to be washed or to rapidly remove dirt materials through enzymatic degradation or the like, as well as seriously important to prevent reattachment of dirt materials that have been once detached from the object to be washed (preventing of redeposition). Particularly, with regard to minute dirt materials such as soot, it is known that if the dirt materials are once diffused in washing water and then are reattached to the object to be washed, it is very difficult to remove the dirt materials. Accordingly, various anti-redeposition agents have been conventionally incorporated into, for example, detergents for clothing products. Examples of the anti-redeposition agents that may be used include cellulose-based compounds such as carboxymethyl cellulose, hydroxypropylmethyl cellulose, and hydroxybutylmethyl cellulose; nonionic polymers such as polyethylene glycol, polyvinyl alcohol, and polyvinylpyrrolidone; and amino acid polymers. However, there have been needs for development of the anti-redeposition agent having a further enhanced effect.
Meanwhile, it has been a traditional practice to incorporate hydrolases such as proteases, lipases and amylases as cleaning aids, into cleaning agents. Cellulases, which constitute one class of hydrolases, are originally known as enzymes that function in neutral to acidic condition, and it has been conventionally considered that cellulases are not suitable to be incorporated into alkaline cleaning agents for clothing. However, in recent years, alkaline cellulases or variants thereof are obtained from plural organisms including thermophilic or alkalophilic bacteria of the genus Bacillus, and the cellulases or variants thereof may also be incorporated into alkaline detergents for clothing (for example, Patent Documents 1 to 6).
Cellulases are enzymes which hydrolyze glycoside bond within β-1,4-glucans including cellulose. Cellulases are mainly produced by bacteria or plants and are available in various kingdoms. Cellulases are classified into endoglucanases (EC3.2.1.4) that degrade cellulose from the interior of the molecule, and exoglucanases (cellobiohydrolases) (EC3.2.1.91) that degrade cellulose from the reduced ends or non-reduced ends of the sugar chain, and release cellobiose. On the other hand, glycoside hydrolases including cellulases are classified into one glycoside hydrolase family, and that family is currently further classified into subfamily 1 to subfamily 108. Cellulases are classified, based on their structures, into families 5, 6, 7, 8, 9, 10, 12, 44, 45, 48, 51, 61, and 74 of the glycoside hydrolase family, and it is also known that the amino acid sequence identity between those families is very low.
However, in recent years, it has been found by analyses of amino acid sequences or three-dimensional structures that cellulases have a common domain having catalytic activity (catalytic domain; CD) and another common functional domain that are linked to each other through a linker. A representative example of the other functional domain is a cellulose binding region having cellulose binding properties (also referred to as cellulose binding module: CBM) (see FIG. 1A). Cellulases usually have plural CBMs. Since cellulose is basically water-insoluble, a cellulase binds to the cellulose surface through the CBMs, and thereby relatively increases the substrate concentration. CBMs are also classified into 40 or more families based on the amino acid sequence identity. In regard to these CBMs, identification of amino acid residues that directly participate in binding to the cellulose has also been carried out (Non-Patent Document 1).
Patent Document 1 discloses a Bacillus sp. strain KSM-S237-derived alkaline cellulase having heat resistance, Patent Document 2 discloses a mutant alkaline cellulase having an optimum pH increased to near pH 10.5, and Patent Document 3 discloses a mutant alkaline cellulase having enhanced productivity. Furthermore, Patent Documents 4 and 6 describe that some of these cellulases show anti-redeposition activity.